Lifecycle Events of DeckGL

To cooperate with Vue lifecycle events, we will expose certain DeckGL life cycle events when the need arises.

The only current example of this is initialRender and using it as a "spinner" or "loading" notifier.

<template>
    <DeckGL>
    @initialRender="()=>{hasDeckLoaded = true}"
    </DeckGL>
    <h1 v-if="!hasDeckLoaded">DECK IS LOADING...</h1>
</template>

<script>
...
data(){
    return{
        hasDeckLoaded: false
    }
} 
...
</script>